Liquid developer for use in electrophotography containing a terpolymer

ABSTRACT

A LIQUID DEVELOPER FOR USE IN ELECTROPHOTOGRAPHY, COMPRISING A TONER DISPERSED IN A CARRIER LIQUID, SAID CARRIER LIQUID CONSISTING OF A HYDROCARBON HAVING A HIGH ELECTRIC RESISTANCE AND A LOW DIELECTRIC CONSTANT AND A SURFACE ACTIVE AGENT DISSOLVED IN SAID HYDROCARBON, SAID TONER BEING PREPARED BY HAVING A VINYL COPOLYMER GRAFT-BONDED ONTO THE PARTICLES OF A PIGMENT OR BY COATING THE PARTICLES OF THE PIGMENT WITH SAID VINYL COPOLYMER, SAID VINYL COPOLYMER CONSISTING OF A LEAST THREE VINYL MONOMRS OF THREE DIFFERENT TYPES SELECTED FROM THE FOLLOWNING THREE GROUPS, RESPECTIVELY, ONE (A) OF WHICH CONSISTING OF VINYL MONOMERS CONTAINING FUNCTIONAL RADICALS HAVING A HIGHLY INCREASED CHEMICAL AFFINITY TO SAID CARRIER LIQUID, THE SECOND GROUP (B) CONSISTING OF VINYL MONOMERS CONTAINING FUNCTIONAL RADICALS WHICH ARE CAPABLE OF CONTROLLING THE POLARITY OF THE PIGMENT EMPLLYED, AND THE LAST GROUP (C) CONSISTING OF VINYL MONOMERS CONTAINING FUNCTIONAL RADICALS WHICH ARE CAPABLE OF PRODUCING TIGHT ADHESION OR FIXING OF THE TONER TO THE LIGHT-SENSITIVE LAYER OF AN ELECTROPHOTOGRAPHIC COPYING MATERIAL.

United States Patent O 3,585,140 LIQUID DEVELOPER FOR USE IN ELECTRO- PHOTOGRAPHY CONTAINING A TERPOLYMER Hazime Machida and Zenjiro Okuno, Tokyo, Japan, as-

siguors to Kabushiki Kaisha Ricoh, Tokyo, Japan No Drawing. Filed June 26, 1968, Ser. No. 740,024 Claims priority, application Japan, July 10, 1967, 42/44,062 Int. Cl. G03g 9/04 US. Cl. 252-621 4 Claims ABSTRACT OF THE DISCLOSURE A liquid developer for use in electrophotography, comprising a toner dispersed in a carrier liquid, said carrier liquid consisting of a hydrocarbon having a high electric resistance and a low dielectric constant and a surface active agent dissolved in said hydrocarbon, said toner being prepared by having a vinyl copolymer graft-bonded onto the particles of a pigment or by coating the particles of the pigment with said vinyl copolymer, said vinyl copolymer consisting of at least three vinyl monomers of three different types selected from the following three groups, respectively, one (a) of which consisting of vinyl monomers containing functional radicals having a highly increased chemical affinity to said carrier liquid, the second group (b) consisting of vinyl monomers containing functional radicals which are capable of controlling the polarity of the pigment employed, and the last group (c) consisting of vinyl monomers containing functional radicals which are capable of producing tight adhesion or fixing of the toner to the light-sensitive layer of an electrophotographic copying material.

BACKGROUND OF THE INVENTION (a) Field of the invention The present invention is concerned with a liquid developer having a markedly increased, stable developability for use in electrophotography, which is prepared by dispersing a toner-which is obtained by either the graftpolymerization, onto the particles of a pigment, of a vinyl copolymer containing specific functional radicals bonded to said copolymer or by kneading said vinyl copolymer with said particles of pigment-in a carrier liquid which consists of a hydrocarbon of petroleum origin having a relatively high electric resistance and a low dielectric constant and containing a small amount of a surface active agent dissolved therein.

(b) Description of the prior art Liquid developers for use in electrophotography, in general, are prepared by dispersing, in carrier liquid consisting of either a paraffinic or isoparaffinic hydrocarbon, a toner which is obtained by kneading the particles of a pigment together with the additives such as a dispersing agent, a polarity controlling agent, a fixing agent, a drying agent and a stabilizer. The toner which was contained in such a liquid developer of the prior art was of a very complicated structure such that the surfaces of the particles of pigment were coated with a complex mixture of the aforesaid various additives, and such a toner had the drawbacks that its polarity became indistinct or that the suspended ICC toner aggregated together and sedimented to the bottom of the carrier liquid during the storage lasting for an extended period of time or during the repeated use of the liquid developer, causing a marked deterioration of the developability of the liquid developer. This deterioration of the developability of the liquid developer is considered to be due to the loss of the balance-which was maintained satisfactorily during the initial period after the liquid developer was manufactured-between the substances which are dispersed in the carrier liquid and the carrier liquid in which these substances are dispersed, said loss of balance taking place on various occasions, for example, when there is a change in the ambient atmosphere in which the liquid developer is stored, or when the exposed copying materials are immersed in the liquid developer during the process of development, or when there occurs the detachment of the additives off the particles of the pigment, owing to the mutual chemical or physical actions between the additives which are coated on or adhere to the particles of the pigment, or due to the degeneration of the additives per se, or to the extremely complicated composition of the toner. Also, the aforesaid addives, in many cases, were composed of those naturally occurring substances such as rosin, asphalt, soya bean oil or linseed oil, so that it was difiicult to obtain additives having uniform chemical properties and a uniform composition. Accordingly, it was difficult to manufacture liquid developers having a uniform developability and uniform quality.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a liquid developer for use in electrophotography whose abilities and properties will not deteriorate during its repeated use or during its storage lasting for an extended period of time.

Another object of the present invention is to provide a liquid developer for use in electrophotography which can be manufactured as products uniform in their quality as well as their abilities and properties, by the use of synthetic substances as the components of the toner, especially by the use of synthetic resins (copolymers) which are bonded to or coated on the particles of a pigment.

In other words, it is the object of the present invention to provide a liquid developer for use in electrophotography which is free of the drawbacks inherent in the conventional liquid developers and which is free of the difliculties encountered in the past in the manufacture of liquid developers having uniform quality, abilities and properties and which, in particular, is of markedly improved developability such as the stability which is exbibited by the liquid developer during its storage and during its repeated use.

According to the present invention, there is provided a liquid developer for use in electrophotography which is manufactured by dispersing a toner in the aforesaid carrier liquid consisting of a hydrocarbon of petroleum origin, said toner being prepared by having a vinyl copolymer graft-copolymerized onto the particles of a pigment such as carbon black (Cl. No. 77266), aniline black, spirit black (Cl. -No. 77267), alkali blue, phthalocyanine blue (C.I. No. 74160), crystal violet (Cl. No. 42555), congo red ((3.1. No. 22120), channel carbon black (C.I. No. 72266) and oil black (Cl. No. 77267), or by kneading said vinyl copolymer with said particles of pigment, said vinyl copolymer consisting of at least three vinyl monomers of different types selected from the following three groups,

(a) alkyl acrylates and methacrylates in which the alkyl has 8 to 19 carbon atoms,

(b) dimethylaminoethyl methacrylate, acrylonitrile, aaminoethyl acrylic acid, a-cyanomethyl acrylic acid, N,N- diphenyl methacrylamide, dimethylaminoethyl acrylate, methacrylonitrile, and diethyl aminomethyl acrylate,

(c) glycidyl methacrylate, benzyl methacrylate, cyclohexyl acrylate, 2-phenoxyethyl acrylate, crotonyl acrylate, Z-phenylethyl methacrylate and 2-phenylethyl acrylate.

The compounds of group (a) have functional radicals having specially markedly increased chemical atiinity to the carrier liquid consisting of hydrocarbons of petroleum origin. By the employment of such a functional radical, the dispersability of the toner can be increased, with the result that the aggregation and the resulting sedimentation of the aforesaid particles of pigment can be markedly arrested. Also, the compound of group (b) possess functional radicals which have chemical afiinity to one of the functional radicals of the surface active agent which is contained in the carrier liquid consisting of a hydrocarbon of petroleum origin, and thus the functional radicals of the group (b) compound adsorb the surface active agent, while another of the functional radicals of the surface active agent which is not adsorbable to the compound of group (b) is disposed on the side of the solvent of petroleum origin, and this another of the radicals of the surface active agent determines the polarity and the interfacial potential of the particles of the pigment. Owing to this arrangement, the polarity of the toner is regulated to be either positive or negative and also there is imparted a sufficient interfacial potential of the toner. In other words, the toner forms, in the liquid developer, the socalled micell structure in which the molecules of the surface active agent are attracted to the toner, resulting in an improvement in the dispersability of the toner in the carrier liquid and also in maintaininng a zeta potential which is sufficient for quickly causing electrophoresis to take place, so that these compounds or group (b) are useful in the formation of a clear copied image on the copying material when the latter is developed. The compounds of group process functional radicals which are capable of exhibiting an action useful in the production of a tight adhesion of the toner onto the lightsensitive layer of the copying material, so that these compounds of group (c) are useful in the fixing of the copied image onto the copying material.

As the carrier liquid in which the aforesaid toner is dispersed and which can be applied to the present invention, it is possible to use any one of the carrier liquids which have been employed in the conventional liquid developers for use in electrophotography in general. More specifically, it is possible to use both of the conventional paraftinic and isoparafiinic hydrocarbons of petroleum origin having an electric resistance of t2-cm or more and a dielectric constant of 3 or smaller. For example, as the isoparafiinic hydrocarbons, the use of those which are sold under the trade name of ISOPAR H (a product of ESSO Standard Oil Inc.) and NAPHTHA No. 6 (a product of Shell Oil Company of USA.) is suitable.

As the surface active agents which are dissolved in the carrier liquid and which can be used in the present invention, there are, for example, those metal salts consisting of naphthenic acid and metals such as manganese, cobalt, nickel, zinc, chromium, magnesium, lead, iron, zirconium, calcium and aluminum; metal salts consisting of such acids as stearic acid, dodecylic acid or palmitic acid and said metals; cationic surface active agents such as lauryltrimethylammonium chloride, stearylbetaine and polyoxyethylene stearylamine; commercial cationic and anionic surface active agents of a wide variety such as the cationic surface active agent which is manufactured and sold by Kao Soap, Ltd. of Japan under the trade name of Farmine, the surface active agent which is manufactured and sold by Gasu Kagaku K. K. of Japan under the trade name of Nikkol, the cationic surface active agents which are manufactured and sold by Mitsubishi Monsant 'K. K. of Japan under the trade names of Santolube 875 and Santolube 393, and the anionic surface active agent which is manufactured and sold by Daiichi Seiyaku K. K. of Japan under the trade name of Lathmit. In case a toner is dispersed in a carrier liquid in which such a surface active agent as mentioned above is dissolved, it is desirable to fisrt disperse a kneaded or graft-copolymerized toner in a hydrocarbon of petroleum origin, the amount of said hydrocarbon being 3 to 5 times that of the toner, and then to add and disperse the resulting concentrated toner liquid (hereinafter to be referred to simply as conc. toner) in a still greater amount of the carrier liquid which consists of the same hydrocarbon. The desirable amount of such a surface active agent which is dissolved in the carrier liquid consisting of said hydrocarbon is in the range of from 10 gr. to 10 gr. per 1000 gr. of the carrier liquid.

As has been described above, the liquid developer according to the present invention has a number of advantages, for example, the toner which is contained in said developer is so firm in the bond between the particles of the pigment and the resin (copolymer) which adheres thereto that there occurs no detachment of the resin from the particles of the pigment. Moreover, the toner is of a very satisfactory dispersability in the carrier liquid owing to the mutual actions between the resin (copolymer) of the toner and the surface active agent which is contained in the carrier liquid. Furthermore, the toner is of a very distinct positive or negative polarity by virtue of the adequate combination of the respective components of the toner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples Examples of 9 kinds of liquid developers for use in electrophotography manufactured according to the present invention are shown in the following Table 1.

The copolymers having the compositions shown in Table 1 were prepared in the following manner. First, the respective component monomers were added to toluene or benzene. To the resulting mixture was added a reaction initiator consisting of azobisisobutylonitrile or benzoyl peroxide in an amount ranging from 0.7% to 1.0% of the total weight of the solvent. The resulting mixture was then subjected to polymerization by heating the same at a temperature ranging from 60 C. to C. for 5 to 10 hours in a nitrogen atmosphere. The kneading which is referred to in the column Graft copolymerized or kneaded in the Table 1 was conducted by placing the vinyl copolymer which was obtained in the manner as has been described above and also particles of a pigment in a ball mill and they were kneaded therein. The resulting kneaded mixture was dispersed in a carrier liquid of an amount 3 to 5 times that of the mixture, and thus a so-called conc. toner was prepared. This conc. toner was then dispersed in a carrier liquid containing a surface active agent dissolved therein, and thus a liquid developer for use in electrophotography was obtained.

On the other hand, the toner which was prepared by the graft-copolymerization of a vinyl copolymer and the particles of a pigment was obtained by first placing the particles of the pigment together with the aforesaid three different types of vinyl monomers in a ball mill or a kneader at the time a vinyl copolymer was synthesized from these monomers; and then in a manner similar to that described in connection with the toner prepared by kneading, they were allowed to react therebetween in the ball mill or the kneader.

For a comparison of the developability with that of the product of the present invention, there were prepared control liquid developers for use in electrophotography in the following manner. To one part by weight of the particles of the pigment, there were added 1 part by weight of a resin which was a copolymer of lauryl methacrylate and dimethylaminoethyl methacrylate, and 0.025 part by weight of a surface active agent which consisted of manganese naphthenate (containing of man- 10 ganese), and the mixture was kneaded. Then, an isoparaffinic hydrocarbon (ISOPAR H) was added to the resulting mixture in an amount 5 times the total weight of said particles of pigment and said resin, and the resulting mixture was dispersed in a ball mill to thereby prepare a conc. toner. Finally, this conc. toner was dispersed in 1000 cc. of a carrier liquid (ISOPAR H).

A comparative test of the respective liquid developers and the respective conc. toners was conducted as will be described in the following paragraphs (A) through (E).

TEST OF CONC. TONERS (A) Each of the conc. toners was stored for a period ranging from 1 to 12 months. At the end of every 1 month, these toners were dispersed in the same carrier liquid,

respectively, to prepare liquid developers. These developers were then used in the developing process. The density of the copied images which were formed on the copying materials were measured to observe the reduction in the density of the copied images due to the deterioration of the polarity of the toner due to the lapse of time. The

result was that the liquid developers of the present invention showed no appreciable deterioration of the polarity at the end of the storage lasting for 12 months. Whereas, a deterioration of the polarity was noted on the control liquid developers at the end of 3 months.

(B) Each of the conc. toners was observed, during the aforesaid test (A), with respect to whether or not there occurred a sedimentation of the toners. The result was that no sedimentation of the toners was noted in the liquid developers of the present invention. However, the control liquid developers showed the sedimentation of the toners at the end of the storage lasting for 3 months.

(C) Each of the conc. toners was applied to a centrifugal separator (rotated at the velocity of 4000 rpm.) to

r coercively cause the sedimentation of the toner, and the amounts of the sedimented toners were compared. The result was that out of 25 gr. of conc. toner, 0.1 gr. sedimented in the case of the liquid developers of the present invention. Whereas, the control liquid developers showed that, out of 25 gr. of conc. toner, 2.5 gr. sedimented.

TEST OF LIQUID DEVELOPERS (D) The respective liquid developers were used in the developing process immediately after they were prepared.

The density of the copied images which were formed on the copying materials was measured. After storing the respective liquid developers for 3 consecutive months, they were used in the developing process to observe how their developability changed due to the storage. The re- 0 sult was that the liquid developer of the present invention showed a reduction in the density of the copied images, which Was noted to be about 7%. Whereas, the control liquid developers showed a reduction of about 30%.

(E) The coeflicient of the light transmission of the respective liquid developers during the periods ranging from immediately after they were prepared till the end of 3 months was measured to observe the aggregation of the toners caused by the storage. The result was that the liquid developers of the present invention showed hardly any change in the coefficient of light transmission. However, the control liquid developers showed that their coefiicient of light transmission increased with the length of the storage owing to the occurrence of the sedimentation of the toner which was caused by the aggregation of em e c r a P r e n O t e h t 5 m a M B ha en. 58.58 .23 E wn daoZ 2 83 e wfioe wi 3203a d 6Q m 8: I: e fie ifiaz ......de... :3 38 $256 66 Ba e fi fi s fi eii sc EE ES E EQ w 635m? 83 32m @5524 38 3223 .eBfiwom 26; m H tool... 25 54 ......de... m6: 8 3 x fiamo TEQB E N 85 mbm fi fi 63 fifi fi fifi o b 3 fieme snen EEQQ 9 8 250235 qm hoenm Q coo; w coo; T3 ou E300 8 250 1m ........8.8 M33 m0 m Aod fiawroma ec awa ea fi 85 g fiemwmeew aom o sd eep EEw ad 32 2 8 s z e84 w 8o; 1: 8 32 53 1:58... is 69 een 5 86 e 3 E22 ac e e fi e e m m gaze saen 85 ie w xonena Q oQoJ u T3 tout... 55550.50 ou Q Qv e53 em s a 33 ve ofliofih waonmhofi 83 fifiheeawpwfiwmowmmo w We a 5 Q 8o e 8e; 3 w mmm nfi p m ew w} 8v M 29 2.25m EM SK 38 312% $58584 Awv heee wgmmmwwfi M Q 25 Q So T3 w w ee- {a fivmee 3 5 i ea ieem 86 2382504 QQ epfiiee emzfieo m fl fii ag 38 fi iw fi fiw eofiw Q8 E m 08; a 83 E: ....m H 2 5 --e e (N & e 20 ee fl H i efi mfzi av ee fi fl m H 332cm 00 52 3 meat 3v 28mm some vegan 63 $65 $.88 $5338 we QQ QQEQ .E Ed i 85 AS m weenww 250m we adm .6 038 oedema m fi 55mm fi w E 5 AQXQQ E QQQ \EQE QQQ 6 $0 8335 M WSQ 2c 85.

What is claimed is:

1. A liquid developer for use in electrophotography,

comprising:

(a) a carrier liquid selected from the group consisting of paraffinic and isoparafiinic hydrocarbons having an electric resistance of not less than 10 Q-cm. and a dielectric constant of not greater than 3;

(b) a small amount of at least one surface active agent dissolved in said carrier liquid and selected from the group consisting of (1) the manganese, cobalt, nickel, zinc, chromium, magnesium, lead, iron, zirconium, calcium and aluminum salts of naphthenic acid, stearic acid, dodecylic acid and palmitic acid, (2) lauryltrimethylammonium chloride, (3) stearylbetainc and (4) polyoxyethylene stearylamine; and

(c) a toner dispersed in said carrier liquid, said toner consisting essentially of fine particles of at least one pigment selected from the group consisting of Carbon Black (C.I. No. 77266), Aniline Black (C.I. No. 77267), Spirit Black (C.I. No. 77267), Alkali Blue (C.I. No. 42555), Phthalocyanine Blue (C.I. No. 74160), Crystal Violet (C.I. No. 42555), Congo Red (C.I. No. 22120), Channel Carbon Black (01. No. 77266) and Oil Black (C.I. No. 77267); and a copolymer prepared by copolymerization of (1) at least one monomer selected from the group consisting of vinyl monomers of the below-mentioned monomer group-(a), (2) at least one monomer selected from the group consisting of vinyl monomers of the belowmentioned monomer group-(b), and (3) at least one monomer selected from the group consisting of vinyl monomers of the below-mentioned monomer group- 8 monomer group-(a):

alkyl acrylates and methacrylates, in which the alkyl has 8 to 19 carbon atoms; monomer group-(b):

dimethylaminoethyl methacrylate, acrylonitrile, a-aminoethyl acrylic acid, a-cyanomethylacrylic acid, N,N-diphenyl-methacrylonitrile and diethylaminomethyl acrylate; and monomer group-(c):

glycidyl methacrylate, benzyl methacrylate,

cyclohexyl acrylate, 2 phenoxyethyl acrylate, crotonyl acrylate, 2-phenylethyl acrylate and 2-phenylethyl methacrylate.

2. A liquid developer according to claim 1, wherein the amount of said surface active agent dissolved in said carrier liquid is in the range of from 10' g. to 10 g. per 1000 g. of said carrier liquid.

3. A liquid developer according to claim 1, in which said copolymer is kneaded with said pigment particles to form a mixture thereof.

4. A liquid developer according to claim 1, in which said copolymer is graft-copolymerized with said pigment particles.

References Cited UNITED STATES PATENTS 3,438,904 4/1969 Wagner 252-621 3,503,881 3/1970 Shinshara 252-62.l

GEORGE F. LESMES, Primary Examiner I. P, BRAMMER, Assistant Examiner U.S. Cl. X.R. 260-41 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 585 140 Dated June 15 1971 Inventor(s) Hazime Machida and Zenjiro Okuno It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, line 8; "crylonitrile" should read -crylamide, methacrylonitrile.

Signed and sealed this 9th day of November 1971.

(SEAL) Attest:

EDWARD M.FLETCHEH, JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Patents FORM P0-1050 (IO-69) USCOMM-DC ans-Im ll 5 GOVERNMENT PRINTING OFFICE I9! O-3ifi-83l 

